—Model differencing is an important activity in model-based development processes. Differences need to be detected, analyzed, and understood to evolve systems and explore alternatives. Two distinct approaches have been studied in the literature: c differencing, which compares the concrete or abstract syntax of models, and semantic differencing, which compares models in terms of their meaning. Syntactic differencing identifies change operations that transform the syntactical representation of one model to the syntactical representation of the other. However, it does not explain their impact on the meaning of the model. Semantic model differencing is independent of syntactic changes and presents differences as elements in the semantics of one model but not the other. However, it does not reveal the syntactic changes causing these semantic differences. ne a language independent, abstract framework, which relates syntactic change operations and semantic difference witnesses. We formaliz...